In further evaluation of our studies of MAO inhibitors, the selective MAO-A inhibitor clorgyline was found to have marked anti-anxiety and anti-dysphoria effects and also to be effective in a different spectrum of depressed patients compared to other MAO-A inhibitors. Anti-anxiety and antidepressant effects of clorgyline correlated most highly with changes in norepinephrine concentratons in cerebrospinal fluid and plasma. In contrast, the significant reductions produeced by clorgyline in CSF levels of 5-HIAA, HVA or MHPG did not correlate with theapeutic responses. In other studies, neuroendocrine studies have contributed to evidence of serotonergic system changes during lithium administration and have added new evidence suggesting that neurotransmitter receptor sensitivity changes may be an important effect of antidepressant drug treatment.